1. Field of the Invention
The present invention relates to a lens barrel and a lens assembly.
2. Background Art
In the related art, for example, in optical instruments, such as a camera, a lens assembly in which optical elements, such as a lens, are fixed to a lens barrel, which is formed from a thermoplastic resin by heat caulking, is used.
For example, Japanese Unexamined Patent Application, First Publication No. 2007-203625 discloses, as such a lens barrel, a lens frame that is formed in a substantially cylindrical shape from a plastic material and includes a lens insertion frame portion and caulking portions. The lens insertion frame portion is formed in a concave portion at one end opening of a substantially cylindrical shape that constitutes the lens frame, the lens is inserted into the end opening, and the lens is positioned in the direction of an optical axis. All four caulking portions protrude from the top face of the peripheral edge of the lens inserted into the lens insertion frame portion around the end opening, and are formed in the shape of projections at predetermined intervals. Additionally, Japanese Unexamined Patent Application, First Publication No. 2007-203625 discloses a lens assembly in which the peripheral edge of the lens is fixed by heat-deforming the caulking portions after the lens is inserted into this lens frame.
Additionally, in a lens assembly that requires high precision, it is well known to provide a caulking portion at the whole periphery of a lens outer edge to firmly fix the lens so that the lens is prevented from moving in the range of a gap from a lens insertion frame portion due to vibration or the like. In recent years, particularly, demands for a larger number of pixels or size reduction of a camera or the like have become stronger. In order to achieve these demands, a higher precision of the fixing precision between the lens and the lens frame is required. Moreover, in order to achieve size reduction and effectively utilize barrel space, a lens having cutouts, such as a D-cut shape, is often used.
Usually, if high precision is not needed in caulking fixation, even in the caulking of such a D-shaped lens, a caulking portion is provided on an overall circular-arc portion out of the outer edge of the lens as in a circular lens, and caulking fixation of the lens is performed. However, if this structure is given, eccentricity in which the lens is apt to move to the side with no caulking portion is readily caused due to a pressing force that acts through the caulking portion during heat caulking. As a measure for high precision for suppressing this eccentricity, in the related art, caulking portions are provided at positions that face each other across the optical axis and the D-cut portion of the lens.
An example of the shape of such a related-art lens assembly is shown in FIGS. 10A, 10B, 10C, and 10D. FIG. 10A is a schematic perspective view showing an example of the configuration of the lens assembly of the related art. FIG. 10B is a plan view as seen from a in FIG. 10A. FIGS. 10C and 10D are a b-b cross-sectional view and a c-c cross-sectional view in FIG. 10B.
A lens assembly 100 is an assembly fixed by heat-caulking a lens 101 to a lens barrel 102. The lens 101 is constituted by a cylindrical lens side surface 101e, and a D-cut surface 101d formed of a plane parallel to an optical axis o.
The lens 101 is a negative meniscus lens including a first lens surface 101a formed of a convex spherical surface, and a second lens surface 101b formed of a concave spherical surface. An attachment reference surface 101c for positioning the lens 101 in the direction of the optical axis is formed on the outer edge side of the second lens surface 101b. The attachment reference surface 101c is a plane orthogonal to the optical axis o.
The lens barrel 102 includes a lens-receiving surface 102a that causes the attachment reference surface 101c of the lens 101 to abut against one end portion of a substantially cylindrical cylinder portion 102b including a through hole 102e at the center thereof.
The lens-receiving surface 102a is a plane orthogonal to a central axis p of the cylinder portion 102b, and is formed at a flange portion that extends radially outward at one end of the cylinder portion 102b. Here, the side surface of the flange portion is constituted by a cylindrical surface and a D-cut surface 102f and is formed with almost the same D shape as the outer shape of the attachment reference surface 101c of the lens 101.
Frame portions 102c having a pair of partial cylindrical surfaces that are gently fitted thereto by inserting the lens side surface 101e of the lens 101 extend in the direction of the optical axis o on an outer edge portion of the lens-receiving surface 102a. 
The pair of frame portions 102c are arranged to face each other across the optical axis o, and cover the lens side surface 101e with central angle sizes of 90°, respectively. For this reason, the pair of frame portions 102c are arranged so as to be plane-symmetrical with respect to a plane s (refer to FIGS. 10B and 10C) and a plane t (refer to FIG. 10B and FIG. 10D) or become 180° axisymmetrical with respect to the central axis p. The plane s, as shown in FIGS. 10B and 10C, is a plane that passes through the central axis p and line c-c of the cylinder portion 102b, and is orthogonal to the D-cut surface 102f. The plane t, as shown in FIGS. 10B and 10D, is a plane that passes through the central axis p and is orthogonal to the plane s.
Additionally, tip portions of the frame portion 102c are thermally deformed by a heat-caulking apparatus after the lens 101 is inserted into the frame portions 102c. Caulking and fixing portions 102d are formed that bias the outer edge portion of the first lens surface 101a in the direction of the optical axis o and hold the lens 101.
In this way, in the lens assembly 100, the lens 101 is pinched in the direction of the optical axis o between the lens-receiving surface 102a and the caulking and fixing portions 102d. Thereby, the attachment reference surface 101c is pressed against and fixed to the lens-receiving surface 102a. 
However, the present applicant has discovered from an experimental study that there are the following problems in a lens frame shape, particularly, in the shape of the lens receiving surface of the lens frame, in order to caulk and fix such a D-cut lens with higher precision.
In a case where the lens 101 is a heat caulking to the lens barrel 102 described above to form the lens assembly 100, the lens 101 is pressed against and fixed to the lens-receiving surface 102a side, with the thermal deformation of the caulking and fixing portions 102d. At this time, a pressing force that acts on the lens 101 from the first lens surface 101a side is a force that is plane-symmetrical with respect to the planes s and t, respectively. Thereby, the eccentricity of the lens 101 is reduced compared to a case where a caulking portion is formed in the shape of the letter C. For example, the average of the eccentricity can be about 5 μm.